This invention is based on a method for connecting thin plates stacked on one another and on an apparatus for performing this method as defined hereinafter.
In a known method and apparatus of this kind (German Offenlegungsschrift No. 31 06 313), the identical generally flat parts stacked on one another are deep drawn over a relatively long path, after which an enlarged stretched area is formed on the side via a lateral extrusion or drawing compression, mechanically chaining the thin plates together somewhat as a rivet would do. To gain sufficient underlying support for a die for the deep drawing, on the one hand, and on the other hand to have enough space available during this same swaging operation for the material that is spread out by being swaged, the bottom die has two outwardly pivotable parts, which are displaced by the material as it flows radially outward during the swaging operation. At the moment in the operation when this pivoting is completed, the deep drawing has already ended, so the bottom die parts are no longer required for deep drawing.
This known technique has the following disadvantages: first, a relatively large "connector button" is created; second, a bottom die tool of this kind, with pivotable parts, can have no more than a relatively short service life given the required high pressure load; third, this apparatus is relatively expensive; fourth, because of the yielding pivoting parts the deep drawing is not of uniform quality, even though these parts are pulled counter to one another when the load is first imposed; and fifth, this bottom die tool, with its moving parts, is extraordinarily vulnerable to dirt, since when chips are produced, which is unavoidable in metal working, the resiliently supported pivoting parts can easily become stuck in the open position, and after that the tool could no longer function properly.
Another method and apparatus for another known type (German Pat. No. 19 42 411) combines a stamping operation and a deep drawing operation. The diameters of the die opening and of the shaping die for the stamping operation correspond to one another, and interspaces appropriate for the deep drawing operation are provided in the form of recesses; a substantial difference from the generic type initially described above is that the edge of the lower sheet-metal layer is upset radially inward during the compression operation. Aside from the disadvantage that with this technique the connection is no longer liquid-tight or gas-tight, it also requires two separate operations, which are also handled in the press apparatus. Not least, a stamping operation means that a considerable weakening of the material connection takes place.